Background: The diagnosis of asthma is based on the presence of symptoms. Lung function measurements such as forced expiratory volume in one second (FEV1), peak expiratory flow (PEF) variability and airway hyperresponsiveness support the clinical diagnosis. However, asthma is still an under- or overdiagnosed disease.
Objectives: The aim of this study was to identify which test(s) is the most valuable for making the diagnosis of asthma by using patients with asthma-like symptoms as a reference population.
Methods: One hundred patients admitted to an asthma outpatient clinic of an education and research hospital and 23 non-smoking healthy control subjects were included in this study. An asthma questionnaire, spirometric tests, monitoring of PEF variability during two weeks, non-specific bronchial challenge test with methacoline, skin prick tests (SPT) with common aeroallergens, measurements of serum total IgE and blood eosinophil counts were applied to all cases.
Results: Sixty of one hundred patients were diagnosed with asthma, whereas the 40 remaining participant were accepted as pseudoasthma due to a diagnosis of another cause for their symptoms. The sensitivity and specificity of the methacholine challenge test was 96.5% and 78.4%, respectively. While the most sensitive test was a methacholine challenge test, the most specific test was the reversibility test. The test with the highest correlation of a positive result and asthma was the reversibility test. However, the highest correlation with a negative result was found with the methacholine challenge test. SPT positivity, serum total IgE and eosinophilia had low sensitivity and moderate specificity. The most specific question was "have you had an attack of shortness of breath that came on during the day when you were at rest at any time?", whereas the most sensitive question was "have you had an attack of shortness of breath that came on following strenuous activity at any time?" In addition, the questions "have you had an attack of shortness of breath that came on following strenuous activity at any time?" and "have you woken up with an attack of wheezing at any time?" had significant correlation with the results of the methacholine challenge test.
Conclusions: We have shown that the methacholine challenge test is the most valuable diagnostic tool for asthma. In addition, there is a significant correlation between the methacholine challenge test and some patient symptoms.